polls: Help creating a poll

[gnprice]

As part of poll support (#164), we should support creating a new poll — to the same degree as Zulip web/desktop does, anyway.

The UI in web/desktop is mostly just that you send a message starting with /poll , with a specified format. See help center: https://zulip.com/help/create-a-poll . So in fact with the prototype today it's already possible to create a poll with much the same experience as on web.

The one piece of assistance web adds, AFAICT, is that if in the compose box you start by typing /, you get a little autocompletion widget:

If you select the "/poll …" option, it fills in a bit of the syntax:

So it'd be good to provide something that matches that experience.